The final witness in Scott Watson’s appeal has been heard as the court now hears submissions from both sides.
Watson, who has been in prison for nearly 25 years, is appealing his convictions for killing Ben Smart and Olivia Hope in the Marlborough Sounds after a 1997 New Year’s Eve party.
On day three of the week-long hearing, lawyers for Watson tried to chip away at the reliability of forensic evidence. Their primary argument was that contamination — or transference — explained the two hairs on Watson’s blanket linked him to his murder victim.
Professor in biochemistry and molecular biology says the forensic evidence is "very strong" but not positive identification. (Source: 1News)
At the 1999 trial, crown expert John Bark said the mitochondrial DNA results provided strong support for one of the hairs being Olivia’s.
Mitochondrial DNA was inherited from the mother, unlike nuclear DNA, which came from both parents.
A professor in biochemistry and molecular biology, Mitchell Holland, from Pennsylvania State University, was asked by Watson’s lawyer, Kerry Cook, if mitochondrial DNA could be considered definitive evidence of identification.
"I don't believe it will ever become a definitive method of identification. Only nuclear DNA testing is able to claim that. It would be unlikely that mitochondrial DNA would reach that level. It provides very strong circumstantial evidence, but it is not positive identification," said Holland.
The Crown successfully argued at trial that two long blonde hairs found on a blanket in Watson's boat were linked to Olivia. (Source: 1News)
Holland said Bark’s statement was "safe" but, to make it clear, he would have added the hair could also be linked to a maternal relative.
"It's important to understand that the match is to Olivia Hope, but also Janice Hope and also any other maternal relatives of Olivia Hope," he said.
The court also heard from the police detective who recovered sample hairs from Olivia’s bedroom.
Richard Rolton visited Olivia’s family home on January 10 to collect hairs. He wore gloves but no other protective gear.
Emeritus professor in forensic science James Robertson was the last expert to be called. He reviewed the notes written by the ESR scientist, Sue Vintiner, who examined the hairs.
"I think they're not the best notes I've ever seen.
"The notes should reflect the work that you've done and they should be sufficiently detailed that an independent observer who has a relevant background would understand what has actually taken place and be able to assess that."
Yesterday, Vintiner was criticised for not changing her lab coat when moving between the sample set of hairs and the ones in question.
Robertson said it was not best practice back in 1998 to change lab coats.
"Generally speaking, people wore the same lab coat day-in, day-out.
"Now, again in best practice, I would not have been examining the recovered hairs and the known hairs in the same room on the same day," he said.
Concerns over the reliability of forensic evidence was the key reason the appeal was referred to the Court of Appeal by the Governor General in the first place. The second ground for the appeal, how the identification of Watson was achieved, was dealt with on Monday.
The Court of Appeal judges decision would most likely be reserved, but there were three options: Dismiss the appeal and Watson stays in jail; quash the convictions and order a retrial; or quash the convictions and not order a retrial, in which case Watson would walk free.
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